1. Field of the Invention
The present invention relates to a method for mounting an IC chip on a substrate on which at least one conductive pattern to be connected with the IC chip is formed, and more particularly to a substrate having an IC chip mounted by the method.
2. Description of the Prior Art
The known methods for directly mounting an IC chip on a printed circuit substrate include a wire bonding method in which an IC chip is fixed on a printed circuit substrate, and thereafter the electrodes of the IC chip are connected with corresponding connection patterns by respective wires; and the face down bonding method in which the electrodes of the IC chip are faced to the printed circuit substrate and are fixed thereto by electrically connecting the electrodes with the printed circuit substrate through bump-like members. (protrusive electrodes).
In the wire bonding method, since wires should be respectively bonded to IC chip electrodes, the number of processes increases with the number of electrodes.
In addition, there is the possibility of short circuits occuring between wires in an IC chip having electrodes at close intervals.
In the face down bonding method, bumps (protrusive electrodes) are formed on either an IC chip or a printed circuit substrate, and exposed electrodes are provided at positions corresponding to the bumps so as to butt against the bumps. Then, respective bumps are faced to corresponding exposed electrodes and squashed by being pressed to be glued on the exposed electrodes tightly, thereby improving the electrical connection.
Conventionally, there is also known a method for directly forming the bumps on the IC chip by plating gold on the exposed electrodes of the IC chip or by evaporating gold thereon, and another method for transferring bumps preliminarily formed on another substrate to the IC chip or printed circuit substrate by heat and pressure. But when directly forming bumps on IC chips, the processes of gold plating or gold evaporation were added and the yield of the IC chips decreased.
When transferring bumps formed on another substrate to IC chips by heat and pressure, the processes of exposing the IC chip to much higher temperatures than the usual hardening temperature of sealing resin, and applying high pressure were essential, therefore generating stress on the IC chips and decreasing the yield.
When transferring bumps formed on another substrate to a printed circuit substrate by heat and pressure, it is necessary to use materials resistant to heat for transfer to the printed circuit substrate, and the cost of the substrate is raised.
Conventionally, IC packages have been employed to mount an IC chip on an uneven printed circuit substrate. However, this has proved disadvantageous because an IC package makes the whole device large. Especially when an IC chip is mounted on molded components, the high-density mounting of the IC chip is required for minimizing the size of devices. Accordingly, the development of a method for mounting IC chips directly on substrates has been desired.